In the context of the MobiSiC project (Mobility engineering for SiC devices) we study 4H-SiC MOSFETs with the aim to get more insight in the C distribution and nature across the SiC-SiO2 interface and to correlate the results with electron mobility measurements. Investigations are based on the combination of structural and compositional analyses carried out by high resolution transmission electron microscopy (HRTEM) and spatially resolved EELS.